Abstract

Both a novel shearing interferometer and the first demonstration of particle image velocimetry(PIV) to the stator-rotor gap of a spinning turbine cascade are presented. Each of thesetechniques are suitable for measuring gas turbine representative flows.The simple interferometric technique has been demonstrated on a compressor representativeflow in a 2-D wind tunnel. The interferometer has obvious limitations, as it requires a clear lineof sight for the integration of refractive index along an optical path. Despite this, it is a crediblealternative to schlieren or shadowgraph in that it provides both qualitative visualisation and aquantitative measurement of refractive index and the variables to which it is dependent withoutthe vibration isolation requirements of beam splitting interferometry.The 2-D PIV measurements have been made in the stator-rotor gap of the MTI high-pressureturbine stage within DERA's Isentropic Light Piston Facility (lLPF). The measurements weremade at full engine representative conditions adjacent to a rotor spinning at 8200 rpm. This is aparticularly challenging application due to the complex geometry and random and periodiceffects generated as the stator wake interacts with the adjacent spinning rotor. The application isfurther complicated due to the transient nature of the facility. The measurements represent a 2-D, instantaneous, quantitative description of the unsteady flow field and reveal evidence ofshocks and wakes. The estimated accuracy after scaling, timing, particle centroid and particlelag errors have been considered is ± 5%. Non-smoothed, non-time averaged measurements arequalitatively compared with a numerical prediction generated using a 2-D unsteady flow solver(prediction supplied by DERA). A very close agreement has been achieved.A novel approach to characterising the third component of velocity from the diffraction rings ofa defocusing particle viewed through a single camera has been explored. This 3-D PIVtechnique has been demonstrated on a nozzle flow but issues concerning the aberrations of thecurved test section window of the turbine cascade could not be resolved in time for testing onthe facility. Suggestions have been made towards solving this problem.Recommendations are also made towards the eventual goal of revealing a temporally andspatially resolved 3-D velocity distribution of the stator wake impinging on the passing rotor.